1. Technical Field
The invention relates to a drive assembly of an agricultural machine with a driving engine, which is connected to a power take off (PTO) output shaft for driving an attachment, wherein the torque taken off at the PTO output shaft is limited to a predefined desired value.
2. Background of the Invention
In the prior art, agricultural tractors are equipped with a driving engine, which in operation drives the wheels to advance the tractor, and a power take-off shaft, which is used to drive attachments, such as agricultural implements or balers. A power take-off gearbox is switched between the engine and the PTO output shaft. Such power take-off gearboxes normally have several transmission stages, which may be selected by an operator, and result in the desired speeds of the PTO shaft. The transmission ratio of a drive transmission inserted into the drive train between the driving engine and the wheels can be charged stepwise or continuously to change the driving speed of the tractor.
In a prior tractor and a baler combination, by measuring the torque at the power take-off shaft of the tractor, information is obtained on the flow rate, which is proportional to the torque, of the material picked up by the baler, and is compared to a desired flow rate. If the desired flow rate is above or below a certain value, the propulsion speed of the tractor is changed by automatically regulating the transmission ratio of the drive transmission. The speed of the driving engine, and consequently, of the power take-off shaft, remains constant. A storage medium (ROM or CD-ROM), found on board the tractor equipped with a device for reading the storage medium, is used to store the flow rates as a function of the transmission stages of the drive transmission and different swath densities. The current flow rate is determined using the measured torque. The train is driven using a comparison between the current flow rate derived from the torque at the power take-off shaft and a preset value for an optimal flow rate. The transmission stage of the drive transmission to be chosen is selected using the ratio, stored in the storage medium, between the flow rate and the transmission stage. Here, it is considered a disadvantage that the described automated control functions only when there is a suitable storage medium used each time for the attachment. If the tractor and the attachment are supplied by different manufacturers, a combined effect in the described manner is accordingly almost impossible. This control is likewise not suitable for other attachments for which there are no measurable flow rates, such as for tilling machines.
Another prior tractor is equipped with a measuring device for recording the torque taken off on a PTO output shaft. The maximum value of the torque at the PTO output shaft is stored by the operator. This may be done by manually entering the values or by selecting the corresponding attachment (cutter bar, root harvester, manufacturer) from a list of attachments stored in the central computer of the tractor, where the appropriate limiting values are stored. To prevent damaging the drive train of the tractor or of the attachment in the event of overloading, a comparison between the torque at the PTO output shaft and the specified maximum value is made. If the maximum value is exceeded, the speed of the internal combustion engine is automatically reduced. One disadvantage is that, in the event of exceeding the allowable torque, the power take-off shaft as well as the traveling gear is driven with less speed. Eliminating a possible congestion in the attachment is also not possible here because, for instance, less material than before is picked up by the intake elements of a baler. Since the speed of the power take-off shaft remains constant in relation to the driving speed, the quantity of material picked up per distance covered remains the same.
Therefore, it is desired to have a drive assembly with an internal combustion driving engine, a PTO output shaft, and a drive transmission, which enables an operator to smoothly set, irrespective of the type and manufacturer of the attachment, a desired or maximum torque at the power take-off shaft and to reduce the traveling speed when the torque is exceeded.